Drobo 16TB issue

Hi all I am having a bit of an issue right now, in fact I am not sure I really trust the drobo I have here, the image below has a couple of weird items that I would like clarified, can anyone give me some insight as to how I have 4 x 1TB drives but I can store 16TB of data??

Damien K

Hi Damien,

you have formatted the Drobo to 16TB, in other words you can put in 4 x 4 TB hard drives into the Drobo (whenever those drives will be available) and you still have only one Drobo icon on your desktop.

See also here: http://support.datarobotics.com/app/answers/detail/a_id/23/session/L3NpZC9TWFExUE8yaw%3D%3D/sno/0

Read the user manual too


That’s called “Thin Provisioning” and it is only available in most of the hi-end SAN and DAS/NAS devices but all models of the Drobo product has this feature. Sure we can trust our Drobo but that doesn’t mean we don’t do our backups of our Drobo to another drives. :wink:

I understand that if I used 4 x 4TB drives and formatted accordingly I would end up with 16TB of space, but, I have only got 4 x 1TB drives installed.

How is that so? Of course I am PROBABLY just stupid… and there is clearly a logical explanation for it.

you can see on the image here–> http://keffyn.com/imgdump/drobo16tb.jpg that I only have 4 x 1TB drives, in fact I just shut it down and pulled one out to check, just to make sure I wasnt being an idiot…

Damien K[hr]
I just re-read the post from Sigi, I think I get it, I have TOLD the Drobo that I would like to host up to 16TB, but I in fact only have 4TB installed?

  • if this is the case I am going in search of some 4TB drives, the 5D MK II in RAW takes up a LOT of room…


correct - you could (in theory - but not yet) format it to be 1000TB… but you will still never be able to put more data onto it than you have actual disk space. (think building a very large garage then putting a little car in it - you can still only fit a small amount in the little cars trunk - but when you buy a huge car - you can put more in its trunk, but wont need to build a bigger garage to put it in)

in order to stop you from copying more data to it than you actually have room for (since OSX doesnt know you dont really have 16TB) when drobo starts to get full (i.e. approaches the actual disk space you have available ) it will start to slow down, when it gets VERY full it will slow to a crawl, o you can never put more data on it than you have room for.

doing it this way means when you add newer/bigger disks to it - you dont need to reformat it - as the operating system thinks it was that big all along.

the largest drives available now are 2TB

seagate are rumoured to be readying a 3TB drive, but it would be wise to wait for DRI to get these drives and test them in drobo and say that they are safe to use, before you test them with your important data.

Hey Docchris:

Here I have question for you, you said that drobo would slow down when it is getting full, is it by design? Windows would not report any warning like “you are running out of space” while you copy more data to the drive exceeds space available since Windows doesn’t know the actual space you have, only Drobo knows that, right?



correct, it is by design of drobo. windows thinks you have a 16tb drive and will carry on trying to put data on it.

after about 85% drobo starts to slow down (both deliberately and also because its getting less efficient)

after 95% its get Very slow and at around 98-99% it essentially stops[hr]
oh, and drobo dashboard will report a warning that you are running out of space, at 85% and 95%

When drobo is 98%-99% and it stops, does it block the disk I/O?

I have done an experiment at home with 500GB and 120GB drive (only two hard drives) and I got 94.97GB space available (shown in DroboDashboard), copy lots of data exceeds the actual space. it slowed down 75% full and slower as reaching the actual capacity. However, I have seen that I have 95.9GB of data (shown in drive’s Properties) copied to drobo. Is this right behavior?



It will just get impossibly slow, like 1kb/sec

In the OS or in Drobo Dashboard? Sometimes the OS will show the file as if the copy was already complete and show the full size, even though it’s nowhere near finished.

kaishao, thank you for the explanation, it makes a lot of sense now, once again I can hold trust in my Drobo, which is good, because I have just ordered a DroboElite.

Damien K

Hi bhiga,

95.9GB was shown in the OS. So sometimes the OS tells the incorrect size of data?



he means that if you have a 10GB drive, and copy a 6GB file to it - it will instantly say it only has 4GB free - as soon as it starts copying - rather than saying you have 9 gb free… 8gb free… 7gb free… as you slowly copy the file over

see what i mean?[hr]
however i think your issue is that drobo counts drive size in binary - and your OS is counting in decimal. so you could put 100GB (dec - as mac OS now counts) onto a drive which only looks to be 96GB (Binary - as drobo and the rest of the planet (excluding drive manufacturers) count) since they are the same amount.

Explanation of binary counting prefixes vs the standard SI prefixes

Unfortunately, as Docchris noted, everybody except Snow Leopard, drive manufacturers, and the TiVo web interface use KB/MB/GB/TB to mean kibi-, mebi-, gibi- and tebi- bytes, or base-2 counts (1 KB = 1024 bytes, 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB).

1 TB (SI, Snow Leopard, drive manufacturers, TiVo web interface) = 1,000,000,000,000 bytes
1 “TB” (every other computer OS) = 1,099,511,627,776 bytes
1 TiB = 1,099,511,627,776 bytes

Thanks, guys.

That makes more sense to me now.